For the purpose of this study, fatigue is conceptualized as a human response to physiological changes that include sleep stage cycles, circadian rhythms, and tissue oxygenation. the study consists of 3 phases over a 5-year tie span. Phase I subjects will include a convenience sample of up to 60 women planning a pregnancy within the year who are studied in a randomized protocol during a follicular and luteal menstrual cycle phase. Phase II involves the first 36 subjects for Phase I who become pregnant. They will be studied during each trimester. Phase III will involve the first 24 subjects from Phase II who complete the study at 3 and 6 weeks postpartum. Aim #1 is to describe and compare sleep, circadian rhythm, and oxygenation characteristics at 7 salient time points for women of childbearing age. Analysis of variance for repeated measures (MANOVA) will be used to test the hypotheses that there will be no significant differences over time in: a) sleep parameters (sleep onset latency, REM onset latency, sleep fragmentation, percent of delta sleep, or percent of REM sleep), b) circadian temperature rhythm (mesor, amplitude, acrophase, c) tissue oxygenation (serum iron binding capacity, hematocrit, hemoglobin, progesterone, B12, folic acid, red blood cells, ad oxygen saturation), or d) fatigue severity scores (Profile of Mood State Subscales and Visual Analogue). Aim #2 is to establish relationships between fatigue severity and physiological variables related to sleep, rhythm, and oxygenation. Pearson correlations will be used to test hypotheses that there will be no significant relationships between fatigue severity scores and measures of sleep, rhythm, or oxygenation. Aim #3 is to establish relationships between fatigue and perinatal complications related to preterm birth as well as postpartum recovery. Spearman's rho will be used to test the hypothesis that there will be no significant relationship between fatigue during the third trimester and the presence of perinatal complications. The goal of this research is to gain knowledge of fatigue as a homan response, knowledge of fatigue's sequela, and knowledge of associations between fatigue and selected physiological parameters for women during reproductive years. This knowledge will contribute to the development and testing of nursing strategies to promote the health of childbearing women by minimizing fatigue and perinatal complications.